THURSDAY, March 5, 2015 (HealthDay News) -- Minorities may be more prone than whites to gaining weight during childhood, which puts them at greater risk for becoming overweight or obese adults, new research says.

In the study, blacks, Hispanics and American Indians were more likely to surpass a normal weight at age 18 than whites were, the study found.

All of this "likely reflects complex relationships between physiology, culture, socioeconomic status, genetics and the environment," said study lead author Christy Avery, an assistant professor of epidemiology at the University of North Carolina in Chapel Hill.

She stressed that "once a person is classified as overweight or obese, it is very difficult for him or her to re-attain normal body weight.

However, because excess weight is tied to "so many chronic diseases, this is another example where an ounce of prevention is literally worth a pound of cure," Avery said.

The findings were to be presented Thursday at an American Heart Association meeting in Baltimore. Research presented at medical meetings should be considered preliminary until published in a peer-reviewed medical journal.

In the study, Avery's team combined three data sets involving more than 31,000 adults. Weight categories were defined according to body-mass index (BMI), a ratio of height to weight.

A BMI of less than 25 is considered normal weight, a BMI of 30 or greater is obese, and a BMI between these is overweight.

Those with a normal weight at age 18 ranged from just 49 percent of American Indians to 73 percent of whites.

From ages 18 to 30, those most likely to move from the normal-weight category to the overweight or obese categories were American Indian males and females, Hispanic males and black females.

The percentage of American Indian males of normal weight dropped by almost 7 percent per year, and the proportion of American Indian females of normal weight dropped 6 percent per year.

Similarly, the number of Hispanic males with normal weight decreased by 5.6 percent per year, and black females with normal weight declined 5.2 percent per year.

Black females typically gained weight the most rapidly -- just over 10 percent of black females who had been overweight at age 18 were obese one year later.

A person's surroundings may be key to weight gain over time, one expert said.

One factor adding to obesity risk is an "obesogenic environment," said Dr. Mitchell Roslin, chief of obesity surgery at Lenox Hill Hospital in New York City. That's an environment where it's easier to gain weight than to remain a normal weight in everyday life, even when doing the normal things everyone else does, he explained.

People in poorer households have the greatest difficulty overcoming the challenge of this environment, Roslin added.

"When you move into the lower socioeconomic groups that are struggling to pay their mortgage, surrounded by fast food establishments, you realize hunger is an acute need and you want to fill that with the most satiating food that costs the cheapest," Roslin said. "It's very expensive to eat healthy, and much cheaper to eat junk foods."

There are also likely genetic and cultural reasons for greater weight gain among these minority groups as well, he said, but many experts agree that genetics is a lesser factor.

"While genetics plays a role in any health outcome, the rapid onset of the obesity epidemic indicates that this is largely a nurture problem, not a nature problem," said Dr. Stephen Lauer, a pediatrician at The University of Kansas Hospital. "We have helped to generate the problem, and need to find ways to reverse it."

Addressing obesity will require multiple approaches, added Dr. Robert Eckel, a professor of medicine at the University of Colorado Denver School of Medicine.

"Health care professionals, dietitians, school systems, churches and the government, to some extent, can all get involved, but it starts in the home," Eckel said. "We need to start at an early age, before puberty, in terms of prevention."

Eating as a family, limiting high-sugar and high-fat snacks and enhancing physical activity are all good strategies, Eckel said, though he acknowledged these goals can be more difficult for single-parent families or low-income families living in less safe neighborhoods.

"The most important thing is that being healthy has to be a goal for the whole family," he said. "You can't just treat the afflicted person. If your kids see you working on your health, they're more likely to work on their health. The whole house has to be healthy."